“How does this shirt look?” Natalie Bergman asks, throwing on a stripped chiffon blouse. It’s Friday night at SXSW, and Bergman, who makes up half of the Chicago-born sibling duo Wild Belle, is picking out her performance outfit backstage while her older brother Elliott plugs in their equipment.

The unsigned act has only released one single, the dubby earworm “Keep You,” but it’s been enough to get people’s attention. The venue Antone’s was packed with music fans who were curious to hear what the duo would sound like in a live setting. “It’s been cool to see the response, and it’s just coming from us,” Elliot says. “It’s just been something that we’ve totally done on our own.”

The project came together after Elliot asked his sister to record some vocals for his Afrobeat band, Nomo, in a Michigan studio. “I brought a couple of my demos,” Natalie recalls. “After hearing the lyrics, Elliot was like, ‘Maybe we should just record some of your other songs here.'” The duo is now putting the finishing touches on their debut LP, which draws from an array of influences from electro-pop to reggae.

On Friday, they were assisted by a guitarist, drummer and bassist, and Natalie breezed about the stage with relaxed bravado while Elliot switched effortlessly between keyboards and sax. Instead of looping voices, they created an organic wall of sound by repeating their vocals without breaths. Of the new tracks played, the standout was “Twisted,” a song inspired by the Seventies Zimbabwe psychedelia of bands like Green Arrows and Hallelujah Chicken Run Band. “It’s about a guy who’s sort of mistreating me and only cares about material things,” Natalie explained.

Wild Belle now reside in Brooklyn, and they say their familial ties make for good band chemistry. “It’s been very nice. We see eye to eye on most things,” says Natalie. Agrees Elliot, “There can be five different people saying five different things about something, and all Natalie and I have to do is look at each other and get it.”